1. Technical Field
The present invention relates to a pattern matching technology. For example, the present invention relates to a pattern matching method and apparatus for identifying the position of a pattern formed on the surface of a sample.
2. Background Art
A pattern matching technology is known as one of the technologies used to measure or test a fine structure on the surface of a sample, such as a semiconductor circuit. The pattern matching technology is a technology of identifying the position of a pattern on the basis of a similarity between a sample image and a reference image referred to as a template.
FIG. 1-1 and FIG. 1-2 slow process procedures that are typically used in pattern matching. FIG. 1-1 shows a process procedure used for registration of a template, and FIG. 1-2 shows a process procedure executed when alignment is performed using the template.
A pattern registration process is started after the alignment reference position coordinates are designated and input to a pattern matching apparatus with a SEM (Scanning Electron Microscope) (step S101). A given point on a semiconductor wafer is input as the alignment reference position coordinates.
Next, the pattern matching apparatus captures an image of a predetermined region on the semiconductor wafer as a template image (step S102). The image capturing position is set manually by a user at a position around the alignment reference position coordinates, for example. Besides, there are also cases where the pattern matching apparatus automatically calculates a region in which a unique pattern exists as the image capturing position.
Next, the pattern matching apparatus calculates a similarity threshold on the basis of the captured template image (S103). The similarity threshold is, when a plurality of regions that are similar to the template image are obtained from a search target image, calculated as an intermediate value between the highest similarity and the next highest similarity. Needless to say, other calculation methods may also be used.
Next, the pattern matching apparatus registers as template information (1) the captured template image, (2) the similarity threshold, (3) the alignment reference position coordinates, and (4) a relative distance between the alignment reference position coordinates and the template image (step S104). FIG. 2 shows a relationship among the template image 201, the alignment reference position coordinates 202, and the relative distance 203 between the template image 201 and the alignment reference position coordinates 202.
Next, a procedure of a matching process will be described. The pattern matching apparatus captures as a search target image an image of a region around the alignment reference position coordinates designated and input in step S101 (step S105).
Next, the pattern matching apparatus searches the search target image for a region that is similar to the template image (step S106). Then, the pattern matching apparatus extracts a region with the highest similarity from the search results (step S107).
Next, the pattern matching apparatus determines if the similarity of the extracted region is above the threshold (step S108). If the result of step S108 is positive, the pattern matching apparatus terminates the alignment process (step S109). Meanwhile, when the result of step S108 is negative, the pattern matching apparatus receives an input/designation of the alignment reference position coordinates (step S110), and then terminates the alignment process (step S109).    Patent Document 1: JP Patent Publication No. 2011-090470A    Patent Document 1: JP Patent Publication No. 2007-103645A